PROJECT (HELLO)
cmake_minimum_required(VERSION 3.5)

set(SRC_LIST main.cpp)
message(STATUS "This is BINARY dir " ${HELLO_BINARY_DIR})  ## PROJECT_BINARY_DIR
message(STATUS "This is SOURCE dir "${HELLO_SOURCE_DIR})   ## PROJECT_SOURCE_DIR
add_executable(hello ${SRC_LIST})  ## note: 在if控制语句中，变量是直接使用变量名引用，不需要${}